Inorganic Chemistry Communications 66 (2016) 15–18
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Inorganic Chemistry Communications
Short Communication
Synthesis, structures and catalytic activities of half-sandwich ruthenium
complexes based on Schiff Base ligands
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Wei-Guo Jia , Hui Zhang, Tai Zhang, Shuo Ling
College of Chemistry and Materials Science, Center for Nano Science and Technology, The Key Laboratory of Functional Molecular Solids, Ministry of Education, Anhui Laboratory of Molecular-Based
Materials, Anhui Normal University, Wuhu 241000, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of half-sandwich ruthenium(II) complexes containing Schiff-base ligands [Ru(p-cymene)LCl] [HL = (E)-
4-X-2-((phenylimino)methyl)phenol, X = H (2a); X = CH3 (2b); X = Cl (2c) and X = Br (2d)] have been
synthesized and fully characterized by 1H and 13C NMR spectra, elemental analyses and infrared spectrometry.
Moreover, the molecular structures of ruthenium complexes 2b and 2c were confirmed by single-crystal X-ray
diffraction methods. These half-sandwich ruthenium complexes are highly catalyzed hydrogenation of nitroarenes
to aromatic anilines to proceed in the presence of sodium borohydride reducing agent in ethanol solvent. Notably,
complex 2c was found to be a very efficient catalyst toward reduction of nitroarene compounds with wide functional
group compatibility and substrate scope.
Received 28 December 2015
Received in revised form 23 January 2016
Accepted 1 February 2016
Available online 3 February 2016
Keywords:
Ruthenium
Complex
© 2016 Elsevier B.V. All rights reserved.
Structure
Nitroarene
Reduction
In the past decades, the half-sandwich ruthenium complexes have
attracted considerable attention as active catalysts in the formation of
C\\C and C\\heteroatom bond [1,2]; second building units for the
assembly of metallomacrocycles [3,4] and anticancer drugs in clinic
trials [5]. Syntheses and characterization of half-sandwich ruthenium
complexes are important research fields in organometallic and inorganic
chemistry. Within the past years, significant progress for half-sandwich
ruthenium complexes' exceptional catalytic abilities has been made in
organic transformation [6–10]. Schiff-base compound is an important
class of ligands that can be easily obtained and modified to attain the
desired steric bulkiness — or electronic properties [11]. Thus, it is an
interesting issue to synthesize half-sandwich ruthenium complexes
with Schiff-base ligands and explore their properties. Heterogeneous
ruthenium-based catalysts as the potential candidate for the hydrogena-
tion of nitroarenes have received more attention for their high activity
[12]. However, the use of well-defined half-sandwich ruthenium
complexes containing Schiff-base ligands as homogeneous catalysts for
hydrogenation of nitroarenes is rare.
structures of 2b and 2c were confirmed by single-crystal X-ray diffraction.
The results indicate that the synthesized half-sandwich ruthenium com-
plexes adopt classic “piano-stool” conformation with a six-membered
metallocycle formed by coordination of the Schiff-base ligands to the
metal centers.
The Schiff-base ligands (1a–1d) were obtained from the condensation
of the corresponding salicyaldehyde and its derivatives with aniline,
respectively, in moderate to good yields according to literature methods
[13]. The dark red half-sandwich ruthenium complexes (2a–2d) were
synthesized by the reaction of [Ru(p-Cymene)(μ-Cl)Cl]2 with two equiva-
lents of the Schiff-base ligands in the presence of K2CO3 in CH3CN under
reflux for 3 h according to Scheme 1. Complexes 2a–2d were isolated as
pure complexes by chromatography on silica gel using EtOAC and
petroleum ether as eluent in yields of 80–90%. All complexes have
been characterized by IR, NMR spectroscopy as well as elemental analy-
ses. The half-sandwich ruthenium complexes are air and moisture stable,
soluble in chlorohydrocarbon, alcohol and acetonitrile solvents.
X-ray crystallographic data has been analyzed for complexes 2b and
2c, both single crystals were obtained using slow diffusion of diethyl
ether into a concentrated solution of the complexes in methanol solution.
The crystallographic data for compounds 2b and 2c are summarized in
Table S1, and selected bond lengths and angles are given in Table S3–5.
The molecular structures of 2b and 2c are shown in Fig. 1 and Fig. 2.
Solutions were performed in a monoclinic P21/n (2b) and monoclinic
P21/c (2c) space groups. As shown in Fig. 1 and Fig. 2, each Ru is
surrounded by one chlorine atom, one nitrogen atom and one
oxygen atom from the Schiff-base ligand and one of the p-cymene rings.
Both the ruthenium centers have six-coordinate geometry expected for
Herein, we have synthesized the half-sandwich ruthenium
complexes containing Schiff-base ligands [HL
= (E)-4-X-2-
((phenylimino)methyl)phenol, X = H (2a); X = CH3 (2b); X = Cl
(2c) and X = Br (2d)] and explored their catalytic activities for
reduction of nitroarenes to aromatic anilines. The half-sandwich
ruthenium complexes catalyst allowed the hydrogenation of nitroarenes
to aromatic anilines to proceed in the presence of sodium borohydride re-
ducing agent with high yields in ethanol solvent. Moreover, the molecular
⁎
Corresponding author.
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